Download 20. Nervous system. Spinal cord

Nervous System.
Spinal cord.
Spinal Cord
• Functions to transmit messages to
and from the brain (white matter)
and to serve as a reflex center
(gray matter).
• Tube of neural tissue continuous
w/ the medulla at the base of the
brain and extends about 17” to
just below the last rib. (Ends at
L1)
• Majority of the SC has the
diameter of your thumb
• Thicker at the neck and end of the
cord (cervical and lumbar
enlargements) b/c of the large
group of nerves connecting these
regions of the cord w/ the arms
and legs.
Spinal Cord
• Surrounded by a single
layered dura mater
and arachnoid and pia mater.
• Terminates in cone shaped
structure called the conus
medullaris.
– The filum terminale, a fibrous
extension of the pia mater, extends to
the posterior surface of the coccyx to
anchor the spinal cord.
• The cord does not extend the entire
length of the vertebral column – so
a group of nerves leaves the inferior
spinal cord and extends downward.
It resembles a horses tail and is
called the cauda equina.
Spinal Cord
• Notice the gross features of
the spinal cord on the right.
• 31 pairs of spinal nerves
attach to the cord by paired
roots and exit from the
vertebral canal via the
intervertebral foramina.
Cross Sectional Anatomy of the Spinal Cord
• Flattened from front to back.
• Anterior median fissure and posterior median sulcus
partially divide it into left and right halves.
• Gray matter is in the core of the cord and surrounded by
white matter.
Anatomy of
Spinal
Nerves
Part I: Spinal cord
1. Organization
- General
- Cauda equina
- Meninges
2. Structure
• Grey matter
• White matter
3. Blood supply
4. Spinal nerves
- Typical n.
- Components
• Cauda equina
• Meninges
• Components: Nerve cells, Processes,
Neuroglia, Blood vessels
• Grey columns: Anterior, Posterior,
Transverse, Lateral
• Posterior horns contain
interneurons.
• Anterior horns contain some
• interneurons as well as the cell
bodies of motor neurons.
– These cell bodies project their axons via the
ventral roots of the spinal cord to the skeletal
muscles.
– The amount of ventral gray matter at a given
level of the spinal cord is proportional to the
amount of skeletal muscle innervated.
•
•
•
Lateral horn neurons are
sympathetic motor neurons
serving visceral organs.
– Their axons also exit via the
ventral root.
Afferent sensory fibers
carrying info from
peripheral receptors form
the dorsal roots of the spinal
cord. The somata of these
sensory fibers are found in
an enlargement known as a
dorsal root ganglion.
The dorsal and ventral roots
fuse to form spinal nerves.
•
Anterior:
– Medial group: skeletal
muscles of the neck and
trunk
– Central group: cervical
and lumbosacral
segments & contains the
phrenic, asccessory and
lumbosacral nuclei
– Lateral group: cervical
and lumbosacral areas
innervating skeletal
muscles of the limbs
•
Posterior:
– Substantia gelatinosa:
concerned with pain,
temperature and touch
– Nucleus proprius: fibers
from white posterior column
associated with
proprioception, 2-piont
discrimination and vibration
– Nucleus dorsalis (Clark’s
column) from C8 – L3/4
proprioceptive endings in
spindles
– Visceral afferent nucleus
from T1– L3 receives
visceral afferent
information
Transverse:
– Contains central
canal that starts in
the MO,
– Inferiorly expands
in the conus
medullaris as the
terminal ventricle:
CSF & ependyma
Lateral:
– From T1–L2/3
– Give rise to
preganglionic
sympathetic fibers
– Similar group in S24 give rise to
preganglionic
parasympathtic
fibres
• Mixture of myelinated nerve fibers, neuroglia
and blood vessels
• Ascending tracts
• Descending tracts
• Ascending and descending tracts with the
same origin, course and termination:
Fasciculus
• Intersegmental tracts
• Myelinated nerve fibers.
• Allows for communication btwn the brain and spinal
cord or btwn different regions of the spinal cord.
• White matter on each side of the cord is divided into
columns or funiculi.
– Typically, they are ascending or descending.
• What does that mean?
• Sensory, contain 1st, 2nd and 3rd order neurons
• Pathways for temperature, pain,
proprioception
• Examples: Spinothalamic tract (lateral &
anterior, fasciculus gracilis and cuneatus);
Spinocerebellar tract (anterior & posterior);
Cuneocerebellat tract.
• Other: Spinotectal, spinoreticular, spinoolivary, visceral sensory
• White matter from the supraspinal centers with 1st,
2nd and 3rd order motor neurons
• Examples: Corticospinal, reticularspinal,
tectospinal, rubrospinal, vestibulospinal, olivospinal,
descending autonomic
•
•
•
From vertebral, posterior intercostal, lumbar, lateral sacral,
ascending cervical, deep cervical, iliolumbar aa.
Posterior spinal a. in close association to posterior spinal roots,
but is insufficient to supply the spinal cord alone
Anterior spinal a. unite to for a single artery on the median
fissure of the spinal cord.
• Radicular a. reinforce the spinal arteries by
entering through the intervertebral foramina
• Larger anterior radicular arteries: A.
radicularis magna (artery of Adamkiewicz)
from the left an intersegmental branch of the
descending aorta, that supplies 2/3rds of the
spinal cord
• Internal (anterior & posterior) venous plexus
• External venous plexus (anterior & posterior)
• Basivertebral and intervertebral veins.
• Posterior (dorsal) root: Supplies synovial joints
of the vertebral column, deep muscles of the
back & overlying skin. Posterior root ganglia:
Sensory, unipolar with satellite cells.
• Anterior (ventral) root: Supplies the remaining
areas: anterior & lateral regions of the trunk
and limbs
• What is the major protection for
the brain?
• There are also 3 connective
tissue membranes called the
meninges:
• Cover and protect the CNS
• Protect blood vessels
• Contain cerebrospinal fluid
• The 3 meninges from superficial
to deep:
• Dura mater
• Arachnoid mater
• Pia mater
•
Functions to transmit messages
to and from the brain (white
matter) and to serve as a reflex
center (gray matter).
• Tube of neural tissue continuous
w/ the medulla at the base of the
brain and extends about 17” to
just below the last rib. (Ends at
L1)
• Majority of the SC has the
diameter of your thumb
• Thicker at the neck and end of
the cord (cervical and lumbar
enlargements) b/c of the large
group of nerves connecting
these regions of the cord w/ the
arms and legs.
•
Surrounded by a single
layered dura mater
and arachnoid and pia mater.
• Terminates in cone shaped
structure called the conus
medullaris.
– The filum terminale, a fibrous extension
of the pia mater, extends to the posterior
surface of the coccyx to anchor the
spinal cord.
• The cord does not extend the
entire length of the vertebral
column – so a group of nerves
leaves the inferior spinal cord and
extends downward. It resembles a
horses tail and is called the cauda
equina.
• Notice the gross
features of the spinal
cord on the right.
• 31 pairs of spinal
nerves attach to the
cord by paired roots
and exit from the
vertebral canal via the
intervertebral foramina.
• Resembles a butterfly.
• 2 lateral gray masses connected by the gray
commissure.
• Posterior projections are the posterior or dorsal horns.
• Anterior projections are the anterior or ventral horns.
• In the thoracic and lumbar cord, there also exist lateral
horns.
• 31 nerves
connecting the
spinal cord and
various body
regions.
•
•
•
•
•
8 paired cervical nerves
12 paired thoracic nerves
5 paired lumbar nerves
5 paired sacral nerves
1 pair of coccygeal
nerves
• Each connects to the
spinal cord by 2 roots –
dorsal and ventral.
• Each root forms from a
series of rootlets that
attach along the whole
length of the spinal cord
segment.
• Ventral roots are motor
while dorsal roots are
sensory.
• The 2 roots join
to form a spinal
nerve prior to
exiting the
vertebral column.
• Roots are short
and horizontal in
the cervical and
thoracic regions
while they are
longer and more
horizontal in the
sacral and lumbar
regions.
• Almost immediately after emerging from its
intervertebral foramen, a spinal nerve will divide into a
dorsal ramus, a ventral ramus, and a meningeal branch
that reenters and innervates the meninges and associated
•
•
•
Each ramus is mixed.
Joined to the base of the ventral rami of spinal nerves in the thoracic
region are the rami communicantes. These are sympathetic fibers
that we’ll deal with shortly.
Dorsal rami supply the posterior body trunk whereas the thicker
ventral rami supply the rest of the body trunk and the limbs.